The present invention relates to radiation delivery devices, and to methods of making such devices. The invention is particularly useful in coronary revasculization therapy to remove vascular obstructions, and therefore is described below with respect to such an application, but it will be appreciated that the invention could also be used in other applications.
Coronary vascular obstructions generally require coronary bypass surgery, but frequently such an obstruction may be removed or reduced by Percutaneous Coronary Revascularization (PCR), such as by "balloon angioplasty". However, such a PCR treatment frequently results in a renarrowing of the vessel, called "restenosis", triggered by the injury to the vessel wall. Thus, the injury itself may trigger a healing response in the form of growth of a new inner lining within the vessel to heal the injured area ("intimal hyperplasia").
Restenosis is commonly treated today by stenting. It has been found, however, that the provision of a stent may actually increase hyperplasia and thereby aggrevate restenosis, rather than reduce it. Moreover, restenosis following stenting is particularly difficult to treat.
Another technique now being investigated for preventing renarrowing of the vessel caused by hyperplasia is by the use of drugs, but this approach introduces other problems relating to the drug used.
At the present time, the application of radiation appears to be the most promising treatment now being examined for the prevention of restenosis following PCR. Radiation has been found to work particularly well in inhibiting new growth as has been shown for years in cancer management. External beam radiation, administered in relatively high doses, has a damaging effect on the patient's body, and therefore this approach does not appear to be suitable for reducing restenosis. However, using low-dosage radioactive sources, such as seeds temporarily implanted or inserted into the patient's body (endovascular brachytherapy), appears to be a promising treatment for the prevention of restenosis following PCR.
U.S. Pat. No. 5,683,345, which issued Nov. 4, 1997, discloses a technique for utilizing a catheter to deliver a radiation source to a desired site in the vascular system. The radiation source is in the form of a plurality of individually sealed seeds which emit beta radiation. These seeds are stored in a hand-held device and are hydraulically moved through a sterile catheter, inserted into the patient's vascular system, to the site in the vascular system to be treated. However, precisely locating radiation elements when moved in this manner is particularly difficult especially when they are to be located at a plurality of different sites. Also, this technique does not permit shielding those body parts which are not to be irradiated during the passage of the radiation-producing elements to the treatment site.